The present invention relates generally to field emitter arrays and field emitter array systems, such as computed tomography (CT) imaging systems. More particularly, the present invention relates to emitter array configurations for field emitter array systems.
A CT imaging system typically includes a gantry that rotates at various speeds to create 2D and 3D images. The gantry contains an x-ray source, such as an x-ray tube that generates x-rays across a vacuum gap between a cathode and an anode. The x-ray source projects a fan-shaped beam that is collimated to lie within an X-Y plane of a Cartesian coordinate system, which is generally referred to as the “imaging plane”. The x-ray beam passes through the object being imaged, such as a patient. The beam, after being attenuated by the object, impinges upon an array of radiation detectors. Each detector element of the array produces a separate electrical signal that is a measurement of the beam attenuation at the detector location. The attenuation measurements from all the detectors are acquired separately to produce a transmission profile.
A desire exists to utilize an x-ray system without a rotating gantry, due to complexity and costs involved therein. One system that does not require a rotating x-ray source includes the use of a large vacuum chamber, which incorporates an electron gun and ring-shaped targets to produce x-rays. An electron beam emerges from the gun, several feet away from the patient, travels a bent path toward and impinges on the target material to produce x-rays. The single fairly high power electron beam sweeps out a circle or ring that surrounds the patient, to produce a “scan” effect. Such a system requires a large vacuum system to enclose the electron beam trajectory and a complicated beam deflection system, to accurately steer the beam.
Another system that does not require a rotating gantry is commonly referred to as a stationary CT (SCT) system. The SCT system provides an x-ray source that reduces the complexity of the scanning system and does not require a rotating x-ray source. However, although the complexity of high voltage high power x-ray tubes is generally due to the vacuum enclosure and the careful preparation of the surfaces and volumes of material that are enclosed therein, the complexity of an SCT system can also be due to the number of activation lines and connections associated with the large number of emitter elements of an emitter array.
An SCT system can utilize hundreds to thousands of electron emitters in the generation of x-rays. Each of the emitter elements is addressed in turn via an associated bias or activation line and at appropriate time intervals. Due to the large number of emitter elements, there can exist an equally large quantity of associated activation lines and connections. The large number of activation lines need to pass through the vacuum chamber of the x-ray source to supply the emitter elements, thus there necessitates a large number of vacuum joints.
There is an unavoidable leak rate associated with any feedthrough device. This leak rate is compensated for through the use of pumps, both active and passive, so that the gas pressures do not rise to values inimical to electron source performance.
Due to the complexity and poor reliability of utilizing such a large number of vacuum joints and the desire to decrease the complexity of an SCT system, there exists a need for an improved system and method of controlling the emitter elements.